1. Field of the Invention
The present invention relates to an external device, and more particularly, to an external device capable of generating a virtual storage device in a computer host.
2. Description of the Prior Art
For expanding the function of the computer system and adapting the requirement of the users, different external devices of the computer are developed. For example, external hard disk or portable storage device can expand the limited storage capacity of the computer system. The external CD-ROM drive or CD-RW drive can expand the function of the computer system accessing the multimedia resource and provide the capability to backup large data. The storage device needs to use a medium device (or a bridge) to communicate with the computer system and transmit data.
Please refer to FIG. 1. FIG. 1 is a block diagram of an external device connected to a computer host according to the prior art. The external device 15 connected to the host 11 receives and stores the data from the host 11. The external device includes a bridge 151 and a storage device 152. The bridge 151 is connected between the host 11 and the storage device 152, for providing a data transmission interface so that the host 11 and the bridge 151 can transmit data according to a first data transmission interface, and the bridge 151 and the storage device 152 can transmit data according to a second data transmission interface. Thus, the data from the host 11, through the bridge 151, can be converted to the data capable of the data transmission with the storage device 152. In addition, the bridge 151 includes a control unit 153 for controlling the operation of the bridge 151 according to the commands of the host 11 and performing the data transmission. The storage can be a hard disk. The storage device is connected to the computer host through the bridge. The bridge is in charge of the signal conversion between the storage device and the computer host. For the computer host, the bridge and the storage device form an external storage device. The bridge can generate an external virtual device through the firmware design, and this virtual device can be a CD-ROM drive. Thus, the computer host will have the virtual storage device besides the real storage device, but actually there is one real external storage device.
The external device in use at present, to generate one virtual storage device or a plurality of virtual storage devices, has to store the virtual device data in the storage device. In this way, the storage capacity of the storage device is decreased, and the data are read in the specific method. The virtual device data stored in the storage device occupies the storage space of the storage device so the user obtains less storage capacity. Moreover, the user may damage the file structure of the storage device when using the physical storage device through other different bridges or on other computer systems.